FIG. 7 is a cross sectional view for illustrating a conventional plasma processing apparatus 30 and FIG. 8 is a plane view for illustrating a slot antenna 5 shown in FIG. 7. The plasma processing apparatus 30 illustrated in FIG. 7 is disclosed in, for example, Japanese Patent Laid-Open Application No. 2005-268763.
In FIG. 7, the plasma processing apparatus 30 includes a processing vessel 1 having a top opening, and the processing vessel 1 is configured by stacking up a chamber 11, an upper plate 12, a spacer 13 and a plate cover 14. These are all made of aluminum alloy. In the processing vessel 1, there is disposed a susceptor 3 for holding a target substrate 2 to be processed. The susceptor 3 is supplied with a high frequency bias signal from an AC power supply 17 installed outside of the processing vessel 1.
In order to achieve a uniform exhaustion in the processing vessel 1, there is formed a ring-shaped space 1A around the susceptor 3. In a bottom portion of the processing vessel 1, there is installed a gas exhaust pipe 16 for exhausting a gas inside of the processing vessel 1 by means of a non-illustrated gas exhaust device such as a vacuum pump or the like. On top of the processing vessel 1, there is disposed a dielectric plate 4 at a position corresponding to the target substrate 2 on the susceptor 3, and also on top of the dielectric plate 4, there is installed a slot antenna 5.
The slot antenna 5 is a radial line slot antenna as illustrated in FIG. 8, and it includes a slot antenna radiation plate 5a of a flat disc shape connected with an outer waveguide of a coaxial waveguide 9. In an opening of the slot antenna radiation plate 5a, there are formed a plurality of slots 5b and a plurality of slots 5c perpendicular thereto, and also there is formed a plurality of installation holes 5d along an outer periphery of the slot antenna radiation plate 5a. On top of the slot antenna 5, there is disposed a wavelength shortening plate 6, and the slot antenna radiation plate 5a is fixed to a cooling plate 7 by firmly driving screws 15 into the installation holes 5d. The cooling plate 7 covers the wavelength shortening plate 6 and the slot antenna 5 to cool the slot antenna 5, and cooling water is supplied therein. The cooling plate 7 is fixed to the plate cover 14 by a cooling plate fixing device 10.
The slot antenna 5 is connected with a microwave output terminal of an external microwave generator 8 via the coaxial waveguide 9, and a ground terminal of the microwave generator 8 is connected with the processing vessel 1. The microwave generator 8 supplies a microwave of, e.g., 2.45 GHz to the slot antenna 5 via the coaxial waveguide 9 from a non-illustrated load matching box. A plasma gas, which is supplied from a non-illustrated gas supply port and discharged to a space 1B, is excited by the microwave from the microwave generator 8.
When performing a plasma process in the plasma processing apparatus 30 configured as stated above, the target substrate 2 is mounted on the susceptor 3 in the processing vessel 1, and the inside of the processing space 1B is kept at a predetermined pressure by supplying a predetermined processing gas to the inside of the processing vessel 1 from a gas inlet while performing an exhaustion through the gas exhaust pipe 16. Further, a high frequency bias is applied to the target substrate 2 by the AC power supply 17, and a microwave generated from the microwave generator 8 is supplied to the slot antenna 5.
The microwave spreads and proceeds between the slot antenna 5 and the cooling plate 7 in a radial direction, while a wavelength thereof is shortened by the wavelength shortening plate 6. By concentrically arranging the slots 5b and 5c and arranging them perpendicular to each other so as to correspond to the wavelength of the microwave proceeding in a radial direction, it is possible to radiate a plane wave having a circular polarized wave to the slot antenna 5 in a substantially vertical direction, so that an electric field is generated at a lower portion of the dielectric plate 4. In this manner, the processing gas inside of the space 1B is converted into plasma, and, a predetermined plasma process is performed on the target substrate 2 by selecting kinds of the processing gases. Patent Document 1: Japanese Patent Laid-Open Application No. 2005-268763